The present invention pertains to pharmaceutical injection devices, and, in particular, to a delay mechanism for an automatic injection device.
Patients suffering from a number of different diseases frequently must inject themselves with pharmaceuticals. A variety of devices have been proposed to facilitate these injections. One type of device is an automatic injection device. This type of device, when triggered by a user, automatically inserts into the user a needle of a syringe that prior to triggering was disposed within the device housing, and then automatically injects a dose of medication through that inserted needle. One known type of automatic injection device then automatically advances a shroud to cover the needle when the dose is completed. In another type of automatic injection device having a configuration more desirable to some, and instead of having an advancing shroud, the device will automatically retract the needle into the housing when the dose is completed. One difficulty with designing an automatic injector with a needle retracting feature is ensuring both that the full desired contents of the syringe have been injected and that the syringe needle is properly retracted into the device housing after use.
International Publication Number WO 2005/115516 explains in additional detail such design difficulty, and further proposes solutions using a type of delay mechanism involving a highly viscous fluid damping. While perhaps functional, these solutions are not without their own shortcomings, such as the delay mechanism being used to transfer force to the syringe during injection.
Thus, it would be desirable to provide a delay mechanism for an automatic injection apparatus that can overcome one or more of these and other shortcomings of the prior art.